Function abs_all

publication/code/chapter01/more_cow_usage.rs:5–12

(input: &mut Cow<[i32]>)

use std::borrow::Cow;

fn abs_all(input: &mut Cow<[i32]>) {
    for i in 0..input.len() {
        let v = input[i];
        if v < 0 {
            input.to_mut()[i] = -v;
        }
    }
}

fn main() {
    // 只读，不写，没有发生复制操作